This invention relates to fluid coupling devices such as coolant unions, and more particularly, to an improved sealing arrangement for coolant unions of the type having a seal assembly including an axially movable seal member.
Fluid coupling devices such as rotating unions are used extensively in high speed drilling and boring transfer operations, in high speed machine tool spindles, in clutch and brake operations, and in other applications where it is necessary to couple the outlet of fluid sources to rotating devices. In high speed drilling apparatus, for example, rotating unions are used to conduct a liquid, such as a water based coolant, from a source of coolant to a rotating drill bit. Rotating coolant unions include a sealing assembly which provides the interface between the outlet of the fluid source which is fixed and the rotating device to which coolant is being supplied. The seal assembly includes a rotating seal member that is mounted on the rotor of the rotating union and a non-rotating seal member that is mounted within the housing of the coolant union. The seal surface of the non-rotating seal member is biased into fluid tight engagement with the seal surface of the rotating seal, typically by a bias spring arrangement. The liquid coolant passing through the coolant union lubricates the seal members to minimize wear. However, when coolant fluid is not provided, a condition referred to in the art to as "dry running", the interfacing surfaces of the seal members do not receive lubrication. Dry running results in increased wear on the seal surfaces of the seal members, particularly at high speed operation. Extended dry run operation will cause scoring of the seal faces, particularly the seal face of the rotating seal member, resulting in leakage around the seal faces which will require replacement of one or both of the seal members. Because the rotating seal member is either permanently attached to the rotor or is integrally formed with the rotor, replacement of a damaged or scored rotating seal member usually requires replacement of the entire rotor assembly.
To solve seal wear problems associated with dry running, rotating coolant unions have been developed in which the rotating seal member is automatically disengaged from the non-rotating seal member in the absence of liquid coolant. Such coolant unions are commonly referred to as "pop-off" unions because the fixed seal member is moved axially relative to the housing of the coolant union out of engagement with the rotating seal member when coolant flow pressure decreases below a selected or predetermined value. The non-rotating seal member is mounted on a carrier that is adapted to be moved to carry the seal member into engagement with the rotating seal member when coolant flow pressure is increased to the selected value.
Because "pop-off" type unions require axial movement of one seal member along the inner surface of the housing of the union, sealing must be provided to prevent leakage forwardly past the axially movable seal member through the gap between the seal member carrier and the housing inner surface on which it slides. In one type of rotating coolant union, such sealing is provided by an O-ring seal, located in an annular groove in the inner surface of the housing, which engages the outer surface of the carrier for the non-rotating seal member about its circumference. However, because the O-ring seal is fixed in an annular groove in the housing, as the carrier axially moves the non-rotating seal member into and out of engagement with the rotating seal member, the seal is dragged along the outer surface of the carrier. The resultant wear on the O-ring seal will cause the O-ring seal to fail, permitting forward flow of the liquid coolant from the inlet of the union into the interior of the housing.
Another example of a "pop-off" type coolant union including a fluid actuated seal assembly is disclosed in U.S. Pat. No. 4,976,282 which was issued to Zbigniew Kubala and which is assigned to Deublin Company of Northbrook, Ill. This coolant union includes a diaphragm in the fluid path for driving the non-rotating seal member into engagement with the rotating seal member when liquid coolant is being supplied to the coolant union. A bias mechanism drives the seal members apart in the absence of liquid coolant. When sufficient coolant pressure is provided, fluid pressure on the diaphragm causes the diaphragm to move the seal member carrier axially to drive the non-rotating seal member into engagement with the rotating seal member. In this coolant union, the diaphragm provides sealing against coolant leakage forwardly of the housing. However, the use of the diaphragm for actuating the seal assembly increases the cost and the complexity of such coolant unions.